Method and means for the removal of liquid or solid particles from a volume of gas

ABSTRACT

There is disclosed a method for the removal of liquid or solid particles from a volume of gas by generating a multiplicity of charged, individual bubbles, the bubbles being substantially larger than the particles, and introducing the charged bubbles into the volume of gas. The bubbles are either hollow liquid bodies or hollow solid bodies. Means are also disclosed for generating and electrically charging bubbles. According to a first embodiment of the invention, the particles are fog droplets and the method and means are used to disperse the fog. According to a second embodiment, the particles are dust particles which exist in the atmosphere, and the method and means are used to collect and remove the dust. According to a third embodiment, the method and means are used to clean dust particles from effluent gases such as those resulting from combustion processes. According to a fourth embodiment, the method and means may be used to collect particles during chemical manufacturing processes.

United States Patent Inventor T. G. Owe Berg 14361 Deanann Place, GardenGrove, Calif. 92640 Appl. No. 833,993

Filed June 17, 1969 Patented Aug. 24, 1971 METHOD AND MEANS FOR THEREMOVAL OF LIQUID OR SOLID PARTICLES FROM A VOLUME OF GAS 3,028,6854/1962 Silverman 3,333,288 8/1967 Ziegler 310/6 UX 15/50R ABSTRACT:There is disclosed a method for the removal of liquid or solid particlesfrom a volume of gas by generating a multiplicity of charged, individualbubbles, the bubbles being substantially larger than the particles, andintroducing the charged bubbles into the volume of gas. The bubbles areeither hollow liquid bodies or hollow solid bodies. Means are alsodisclosed for generating and electrically charging bubbles. According toa first embodiment of the invention, the particles are fog droplets andthe method and means are used to disperse the fog. According to a secondembodiment, the particles are dust particles which exist in theatmosphere, and the method and means are used to collect and remove thedust. According to a third embodiment, the method and means are used toclean dust particles from effluent gases such as those resulting fromcombustion processes. According to a fourth embodiment, the method andmeans may be used to collect particles during chemical manufacturingprocesses.

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INVENTOK T. G. OWE BERG ATTORNEYS METHOD AND MEANS FOR THE REMOVAL OFLIQUID OR SOLID PARTICLES FROM A VOLUME OF GAS BACKGROUND OF THEINVENTION l. Field of the Invention The present invention relates to amethod and means for the removal of liquid or solid particles from avolume of gas and more particularly, to a method which utilizes charged,individual bubbles to attract and remove liquid or solid particles froma volume of gas.

2. Description of the Prior Art Many situations exist in which it isdesirable to be able to remove liquid or solid particles from a volumeof gas in which they are suspended. For example, removal of solidparticles in the form of dust may be required in mining operations, suchas coal mining, wherein very small coal particles represent a serioushealth hazard. Removal of liquid or solid particles may also be requiredin chemical manufacturing processes in which an undesirable mist oftenforms. The ability to remove liquid particles would be invaluable in thedispersal of fog which is caused by the suspension of a plurality ofdroplets of liquid in the atmosphere. Finally, many situations exist inwhich it is necessary to physically separate and remove dust particlesfrom effluent gases in which they are suspended. As examples, suchseparation may be required: (i) to collect a product which has beenprocessed or handled in gas suspension, as in spray-drying or pneumaticconveying; (2) to recover a valuable product inadvertently mixed withprocessing gases, as in kiln or smelter exhausts; (3) to eliminate anuisance, as in fly-ash removal; (4) to reduce equipment maintenance, asin engine intake air filters; (5) to eliminate a health, fire, explosionor safety hazard, as in bagging operations or nuclear separations plantventilation air; and (6) to improve product quality, as in cleaning ofair used in processing pharmaceutical or photographic products.

Many particle collection systems have been developed for separating andremoving particles from a volume of gas. Generally, most systemsexisting today depend upon subjecting the suspended particles to someforce which will drive them to a collecting surface or surfaces.However, although many of the examples cited above are suited for suchremoval techniques, many other situations are not. For example,conventional particle collection systems are ineffective in thedispersal of fog which is nothing more than water droplets suspended inthe atmosphere. Because of the large volume of air involved,conventional particle collection systems are incapable of dealing withthe problem.

Another example is in mining operations and especially in coal miningwhere it would be desirable to be able to remove the coal dust from theatmosphere without first removing the atmosphere from the room,processing the atmosphere, and returning it. For this reason, someattempts have been made to clean the coal mine atmosphere by sprayingwater into the coal mine. This technique relies on the known theory thatfalling droplets of water are scavengers of dust particles. Improvedresults have been obtained by placing a charge on the water dropletssince the charge increases the collection efficiency of the droplets.However, this technique has not been very effective because of the greatrelative velocity of a spray drop that is large enough to carry asubstantial charge. Although the particles to be scavenged may beattracted to the spray drop and accelerated to a velocity far above thatin free fall, they are not likely to reach a large enough velocity tocatch up with the falling spray drop. If the scavenger were large enoughto carry a large charge and at the same time had a small fall velocity,it would be much more effective as a scavenger.

The use of spray drops in spray towers and scrubbers is based uponcollection by impaction as a result ofinertia. As a consequence,increased collection efficiency is sought by increasing the dropvelocity. However, very small particles, of less than lp., virtuallylack inertia and cannot be scavenged in 2 this manner. The collectionefficiency of conventional equipment based on this principle is verypoor for small particles.

The general principles outlined above are known. For example, it isknown that hailstones and snowflakes are more effective scavengers ofatmospheric particulates than are rain drops. The invention pertains tothe generalization and the utilization of these principles for practicalpurposes. SUMMA- RY OF THE INVENTION The present invention overcomes thedeficiencies of present methods for the removal of liquid and solidparticles from a volume of gas. It hereby produces a collectionefficiency that exceeds that of conventional methods by orders ofmagnitude.

The present invention is based upon a combination of two principles:electrostatic attraction by the scavenger of the particles to bescavenged, and a small relative fall velocity of the scavenger combinedwith a large size and a large charge. The application of theseprinciples leads to the use of bubbles as scavengers. They offer theadditional advantage that their fall, or rise, velocity can becontrolled, e.g. by a choice of gas or gas temperature inside thebubble.

Therefore, and in accordance with the present invention, liquid or solidparticles maybe removed from a volume of gas in which they are suspendedby generating a multiplicity of bubbles, the bubbles being substantiallylarger than the particles, and introducing the bubbles into the volumeof gas.

It is, therefore, an object of the present invention to provide a methodfor the removal of liquid or solid particles from a volume of gas.

It is a further object of the present invention to provide a method forthe dispersal of fog.

It is a still further object of the present invention to provide amethod for the removal of dust particles from a volume of f gas.

It is another object of the present invention to provide a method forthe removal of coal particles from a coal mine.

It is still another object of the present invention to provide a methodfor collection of liquid and solid particles during the manufacture ofchemical elements, compounds and solutions.

Another object of the present invention is the provision of means forgenerating electrically charged bubbles.

Still another object of the present invention is the provision of amethod for the removal of liquid or solid particles from a volume of gasby generating a multiplicity of charged, hollow, liquid or solid bubblesand introducing the bubbles into the volume of gas.

Still other objects, features and attendant advantages of the presentinvention will become apparent to those skilled in the art from areading of the following detailed description of the preferredembodiments, taken in conjunction with the accompanying drawingswherein:

BRIEF DESCRIPTION OF THE DRAWINGS The sole FIGURE shows a machine forthe production of bubbles to which a charging device has been added.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before proceeding with adiscussion of the specific embodiments of the present invention, itshould be mentioned that techniques for blowing bubbles per se are oldand well known in the art. Many different types of liquids and gases maybe used to generate bubbles depending upon the stability required. Fordiscussion of the various possible liquids and gases available forbubbles and a discussion of the historical development of experimentswith bubbles, reference should be had to an article entitled How to BlowSoap Bubbles That Last for Months or Even Years by C. L. Strong inScientific American, May, 1969, Volume 220, No. 5, pages 128-134. Itshould also be mentioned that when using the word bubble there is notonly included the ordinary hollow liquid bodies made from soap or someother liquid solution, but there is also included hollow, solid bodiessuch as hollow spheres made from plastic, glass, or other materials,since in both cases, the results will be the same.

Referring now to the sole FIGURE of drawings, there is shown aconventional bubble generator, generally designated 10, which has beenmodified to incorporate means to increase the charge on the bubble.Bubble generator includes a bubble formula reservoir 12 which is,essentially, a rectangular housing having a partially open top at 14.Contained within reservoir 12 is a suitable liquid 16 which is used tomake the bubbles. Reservoir 12 is partially enclosed at the top thereofby a cover 18 which supports a motor 20. Motor 20 includes a shaft 22which rotatably supports a circular disc 24 which includes a pluralityof holes 26. Disc 24 partially extends into opening 14 in reservoir 12so as to be partially submerged within bubble formula 16. The remainingportion of bubble generator 10 is a blower positioned within a blowerhousing 32. Blower housing 32 has a first side 34-which is positionedparallel to and spaced from disc 24. Side 34 has a plurality of holes 36therein. Blower housing 32 has a second side 38 which has a singleopening 40 therein. Finally, blower 30 is rotated by suitable drivemeans 42.

In operation, blower 30 is rotated by drive means 42 thereby drawing airor another gas through opening 40 in side 38 of housing 32 and sending astream of gas through holes 36 in side 34. Simultaneously, motor 20rotates disc 24 through bubble formula 16. As holes 26 in disc 24 emergefrom reservoir 12, they are coated with bubble formula 16. The air orother gas coming through holes 36 passes through holes 26 in disc 24blowing the bubbles.

According to the present invention, such a conventional bubble generatormay be modified to substantially increase the charge on the resultantbubbles by adding a plate 44 which is supported by insulators 46 and 48above cover 18 ans spaced from disc 24, on the opposite side of disc 24from side 34 of blower housing 32. A source of DC voltage 50 has a firstterminal connected to plate 44 and a second terminal connected via aslip ring assembly or other conventional means to disc 24. In thismanner, a voltage potential is created between disc 24 and plate 44thereby creating an electrostatic field therebetween. Because of thelocation of plate 44, the bubbles emerging from holes 26 in disc 24 passinto this field and are charged accordingly. The polarity of the chargecan be adjusted by proper selection of the polarity of voltage supply50.

It should be emphasized that bubble generator 10 is a well known machinefor the production of bubbles to which a charging device has been added.Bubble generator 10 constitutes essentially a point source of bubbles.In other applications, line sources, surface sources or volume sourcesmay be preferable. In these cases, available bubble generators may bemodified in a similar manner so that the emergent bubbles pass throughan electrostatic field upon generation to increase the charge thereon.

With these principles in mind, it is the basic teaching of the presentinvention that liquid or solid particles may be removed from a volume ofgas in which they are suspended by generating a multiplicity of chargedbubbles, the bubbles being substantially larger than the particles,introducing the charged bubbles into the volume of gas where the bubbleselectrostatically attract the particles, and removing the bubbles withthe particles from the gas by conventional means including permittingthe bubbles with the particles to precipitate out of the volume of gas.In addition, in most embodiments which make use of this principle, it isimportant that the bubbles be individual bubbles rather than in the formofa foam.

According to a first embodiment of the present invention, the basicmethod, and the apparatus of the FIGURE, may be used to disperse fog. Ingeneral, fog consists of water droplets. Studies appear to indicate anessentially uniform droplet charge, e.g. predominantly negative. Thedroplets then tend to repel one another, and this effect may contributeto the stabili ty of the fog.

Almost any disturbance of the air will cause coalescence of the waterdroplets which form the fog. Therefore, by introducing a multiplicity ofbubbles into the fog, the bubbles having a diameter of 100 to 1,000times the diameter of the fog droplets, and by placing a charge on thebubbles which is preferably opposite to the charge on the fog droplets,the fog droplets will be attracted to the bubbles. Because of the greatdifference in size between the bubbles and droplets, each bubble will becapable of attracting many fog droplets. As a large number of fogdroplets adhere to the bubble, the entire mass becomes heavy andeventually precipitates out. Typically, after a large number of fogdroplets have adhered to the bubble, the bubble and fog dropletscoalesce forming a large droplet which precipitates out.

In a typical application, a curtain of bubbles is produced by knownmeans such as that described previously. The bubbles are released upwindof the fog area to be cleared so that they drift with the wind into thefog area, sweeping up the fog droplets. The bubbles are preferablyintroduced in the form of individual bubbles. However, the bubbles mayconceivably be introduced in the form of a foam. A suitable risevelocity or rate at which the bubbles will rise into the fog iscontrolled by selection of the nature and the temperature of the gasinside the bubbles. When making this selection, however, considerationmust also be given to the fact that the gas will also influence thelifetime ofthe bubbles.

According to a second embodiment of the present invention, the basicmethod for the removal of liquid or solid particles from a volume of gasmay be used to remove solid particles in the form of dust from theatmosphere. With respect to the collection of dust, it should be notedthat the collection efficiency of a droplet of water is a function ofthe diameter of the dust particles sought to be collected. In otherwords, as the diameter of the particle increases, so does the collectionefficiency of the water droplet. Conversely, very small particles,having a diameter ofless than 2 microns, are the most difficult toremove from a volume of gas. Furthermore, it is these small particleswhich are the most harmful since they are the ones which most easilyfind their way into the lungs. Because of these factors, the presence ofvery small dust particles presents serious problems in many situations.One example would be in mines and especially coal mines where the air ishighly contaminated with dust particles.

According to the present invention, a charged-bubble generator may belocated in -a coal mine and a liquid and gas selected for the bubblesthat are completely safe to man. The bubbles may then be generated andintroduced into the mine whereupon the particles will be attracted tothe bubbles. It should also be noted that since the bubble is severalorders of magnitude larger than the dust particle, each bubble will beeffective in collecting a large number of particles. As the particlesadhere to the bubble, the weight of the bubble increases until thebubble and particles simply drop to the ground.

According to a third embodiment of the present invention, the basicmethod for the removal of liquid or solid particles from a volume of gasmay be utilized in a manner similar to conventional particle collectionsystems to remove liquid or solid particles from flowing gases in whichthey are suspended. For example, if it is desired to clean an effluentgas, such as that resulting from a combustion process, the gas may bepassed through a suitable tank. In addition, means such as thatdescribed previously may be provided to introduce a multiplicity ofcharged, individual bubbles into the tank. For the reasons describedabove, the solid or liquid particles will be attracted by the chargedbubbles and the bubbles and particles will drop out of the gas. Undersuch circumstances, the charged bubbles have a very high collectionelficiency since their lightness causes them to float along with the gasthereby staying within the gas until they have collected a large numberof particles.

According to a fourth embodiment of the present invention, the basicmethod for the removal of liquid or solid particles from a volume of gasmay be used to remove the particles which often result during manychemical manufacturing processes. For example, in the manufacture ofsulfuric acid, a mist of H often forms above the body of water which theS0 is to be mixed with to form the acid. According to the presentinvention, this mist may be transferred to the bulk water by introducinga multiplicity of charged, individual bubbles into the H 80 mist. Theliquid particles of H 80, adhere to the bubbles and eventually drop intothe water solution. It should be noted that since a bubble contains lessliquid than a water droplet, less contamination of the resultantsulfuric acid results using the present method than would result ifwater droplets were used to scavenge the H 80 particles.

It can, therefore, be seen that in accordance with the present inventionthere is described a method for the removal of liquid or solid particlesfrom a volume of gas which is both practical and results in collectionefficiencies which are much higher than that obtainable in the priorart. In addition, the present method is capable of several uses in whichprior art collection removal techniques have been ineffective.

While the invention has been described with respect to severalembodiments, it will be apparent to those skilled in the art thatvarious modifications and improvements may be made without departingfrom the scope and spirit of the invention.

I claim: 1. A method for the removal of liquid or solid particles from avolume ofgas comprising the steps of:

generating a multiplicity of charged, individual bubbles,

said bubbles being substantially larger than said particles;

introducing said charged bubbles into said volume of gas whereby saidbubbles electrostatically attract said particles; and

permitting said bubbles with said particles to precipitate out of saidvolume of gas.

2. A method according to claim 1 wherein said bubbles are hollow, liquidbodies.

3. A method according to claim 1 wherein said bubbles are hollow, solidbodies.

4. A method according to claim 1 wherein said particles are dustparticles.

5. A method according to claim 1 wherein said particles are fog dropletsand wherein said volume of gas is the atmosphere. 6. A method for thedispersal offog comprising the steps of: generating a multiplicity ofcharged bubbles, said bubbles being substantially larger than the fogdroplets; dispersing said charged bubbles into said fog whereby saidbubbles electrostatically attract said fog droplets; and permitting saidbubbles with said fog droplets to coalesce and precipitate out of saidfog. 7. A method according to claim 6 wherein the step of dispersingsaid charged bubbles into said fog comprises the step of:

dispersing said bubbles into the atmosphere upwind of the areacontaining said fog whereby said bubbles drift with the wind into saidfog.

8. A method according to claim 6 wherein the polarity of the charge onsaid bubbles is opposite to the polarity of the charge on said fogdroplets.

9. A method for the dispersal of a liquid or solid particle mist duringchemical manufacturing processes comprising the steps of:

generating a multiplicity of charged, individual bubbles,

said bubbles being substantially larger than the particles in said mist;

introducing said charged bubbles into said mist whereby said bubbleselectrostatically attract said particles; and permitting said bubbleswith said particles to precipitate out of said mist.

10. A method for the removal of liquid or solid particles from a volumeof gas comprising the steps of:

passing said volume of gas through a chamber;

introducing a multiplicity of charged, individual bubbles into saidchamber, said bubbles floating along with said volume of gas andattracting said particles; and

removing said bubbles with said particles from said volume of gas byconventional means.

11. Apparatus comprising:

means for generating a multiplicity of bubbles; and means forsubstantially increasing the electrical charge on said bubbles thatnaturally occurs during generation thereof.

12. Apparatus according to claim 11 wherein said means for electricallycharging said bubbles comprises:

means for establishing an electrostatic field, said bubbles passingthrough said field.

13. Apparatus according to claim 11 wherein said means for substantiallyincreasing the electrical charge on said bubbles is operative toincrease, by several orders of magnitude, the electrical charge thatnaturally occurs during generation of said bubbles.

14. A method for the removal of liquid or solid particles from a volumeof gas comprising the steps of:

generating a multiplicity-of charged, individual bubbles,

said bubbles being substantially larger than said particles;

introducing said charged bubbles into said volume of gas whereby saidbubbles electrostatically attract said particles; and

removing said bubbles with said particles from said volume of gas byconventional means.

2. A method according to claim 1 wherein said bubbles are hollow, liquidbodies.
 3. A method according to claim 1 wherein said bubbles arehollow, solid bodies.
 4. A method according to claim 1 wherein saidparticles are dust particles.
 5. A method according to claim 1 whereinsaid particles are fog droplets and wherein said volume of gas is theatmosphere.
 6. A method for the dispersal of fog comprising the stepsof: generating a multiplicity of charged bubbles, said bubbles beingsubstantially larger than the fog droplets; dispersing said chargedbubbles into said fog whereby said bubbles electrostatically attractsaid fog droplets; and permitting said bubbles with said fog droplets tocoalesce and precipitate out of said fog.
 7. A method according to claim6 wherein the step of dispersing said charged bubbles into said fogcomprises the step of: dispersing said bubbles into the atmosphereupwind of the area containing said fog whereby said bubbles drift withthe wind into said fog.
 8. A method according to claim 6 wherein thepolarity of the charge on said bubbles is opposite to the polarity ofthe charge on said fog droplets.
 9. A method for the dispersal of aliquid or solid particle mist during chemical manufacturing processescomprising the steps of: generating a multiplicity of charged,individual bubbles, said bubbles being substantially larger than theparticles in said mist; introducing said charged bubbles into said mistwhereby said bubbles electrostatically attract said particles; andpermitting said bubbles with said particles to precipitate out of saidmist.
 10. A method for the removal of liquid or solid particles from avolume of gas comprising the steps of: passing said volume of gasthrough a chamber; introducing a multiplicity of charged, individualbubbles into said chamber, said bubbles floating along with said volumeof gas and attracting said particles; and removing said bubbles withsaid particles from said volume of gas by conventional means. 11.Apparatus comprising: means for generating a multiplicity of bubbles;and means for substantially increasing the electrical charge on saidbubbles that naturally occurs during generation thereof.
 12. Apparatusaccording to claim 11 wherein said means for electrically charging saidbubbles comprises: means for establishing an electrostatic field, saidbubbles passing through said field.
 13. Apparatus according to claim 11wherein said means for substantially increasing the electrical charge onsaid bubbles is operative to increase, by several orders of magnitude,the electrical charge that naturally occurs during generation of saidbubbles.
 14. A method for the removal of liquid or solid particles froma volume of gas comprising the steps of: generating a multiplicity ofcharged, individual bubbles, said bubbles being substantially largerthan said particles; introducing said charged bubbles into said volumeof gas whereby said bubbles electrostatically attract said particles;and removing said bubbles with said particles from said volume of gas byconventional means.